The History is a rolling record of the book outs. It is 50 book outs long. As the 51st book out is added, the oldest book out in the History is deleted.
It is not possible to clear or empty the History.
If you want to keep a sub-set of the all the book outs done, we recommend adding additional tabs to the Clipboard, and changing the default Clipboard names to something that is more meaningful for you.